1. Technical Field of the Invention
This invention relates to printed articles having light-storing printed layers and label sheets having such light-storing printed layers for use in indicating information and the like on audio and video tape cassettes and other recording media such as MDs, MFDs, and CDs, or on cases of paper or plastics holding those media for storage. The invention also relates to articles provided with such light-storing printed layers.
2. Prior Art
Audio and video tape cassettes, MDs, and other disc cassettes are furnished with label sheets which the user can affix, after inscription of appropriate information or the like, to the casings or housings of the cassettes themselves or to the cases containing the cassettes. These housings and cases usually have receptive areas for labeling, each consisting of a recess to which a label can be attached. The user writes information on the label with a pencil, ballpoint pen, or other writing implement, and then sticks it on each cassette housing or each case for the housing, or vice versa. Each label has a blank space to be filled out with a subject of the contents, title of music, or other information, besides identification marks and other inscription that facilitate the user's choice according to the intended use.
FIG. 1 is a perspective view of a conventional audio tape cassette, showing a label 2 affixed to the cassette housing 1, with a blank surface 5 to be filled out. FIG. 5 is a cross sectional view indicating a typical structure of prior art label sheet 2. A writable label base 3 is lined with an adhesive layer 7, which in turn is protected on the opposite side with release paper 9. Before use, the release paper 9 is peeled off, and the label base 3 with the adhesive layer 7 is attached to the cassette housing 1 in the correct position.
The ink commonly used in printing writable label sheets is an offset or silk screen printing ink of ordinary composition for identification of sides A and B and for decorative designing of cassette housings 1. The ordinarily printed labels are identifiable and legible in the sunlight or illumination, but not in the dark. As an additional user-oriented feature, there is a growing demand for labels as useful at night, particularly in the dark, as in the light.
Some approaches have been made to meet the demand. One approach, as typically proposed by Japanese Utility Model Application Kokai No. 62-80282, uses a light-storing, phosphorescent paint in giving identification and indication directly to the both sides A and B of cassette housings so that the user can clearly differentiate between the two sides in a dark place.
Another approach, as according to Utility Model Application Kokai No. 59-142981, offers a label consisting of a label base, a self-emitting, luminous paint layer formed on the base surface, and a scratchable layer formed further on it by opaque printing.
Further, EP0700046A2 (Japanese Patent Application Kokai No. 8-77746) proposes to apply a light-storing printed layer having a light-storing property over about eight hours in which calcium carbonate or protein powder is mixed on a label sheet to be attached to a cassette, or directly on a cassette using a screen printing method, in order to impart both the light-storing property as well as the writing property to the light-storing layer on which letters or symbols may be directly written with a writing instrument like a pencil.
A few more techniques have been introduced to help distinguish letters and alphanumerical symbols on part of cassette housings, such as of magnetic tape cassettes, by printing them in white ink or light-storing ink.
For example, Japanese Patent Application Kokai No. 63-117383 came up with a liner sheet base containing a light-storing pigment so that the tape condition inside the cassette can be observed in the darkness.
Problems to be Solved
The use of phosphorescent paint in direct inscription as proposed by Utility Model Application Kokai No. 62-80282 does not allow the user to write necessary information on the cassette.
The label according to Utility Model Application Kokai No. 59-142981 that comprises a self-emitting, luminous paint layer formed on the base, and a scratchable layer formed further on the paint layer, has also drawbacks. The implement for scratch writing must have a hard point free of ink, something like a stylus; otherwise the scratched surface would be so stained that the luminous paint layer might become indiscernible. In addition, the scratch powder scatters, sometimes seriously marring the appearance and quality of inscription giving necessary information.
The attempt in EP0700046A2 to overcome these drawbacks is to provide a luminous or light-storing printed layer on the label base surface or on the cassette housing, and enable the user to write with a pencil or other writing implement directly on the printed layer surface. However, the luminous or light-storing pigment, which consists of a mass of hard and large inorganic particles, forms such a coarse label surface that the information written with a pencil is difficult to erase. Ballpoint pens and fountain pens are of little use on that surface because it repels ink. Felt-tip pens are useless either, since the tip is easily worn out by the abrasive action of the coarse pigment particles.
It is already in practice to form a light-storing layer on not only tape cassette housings but also on other articles by printing with an ink based on a light-storing pigment (i.e., a light-storing ink) and then print letters, figures, and patterns in black on the light-storing layer so that the letters and other inscriptions become visible under luminescent backgrounds at night or in a dark room. The most important of factors determining the success of arrangements is the remanent luminescence time of the light-storing layer. The light-storing paint is required to maintain a remanent luminescence period of at least 8 hours in which the letters, figures, and patterns are discernible. In respect of remanent luminescence, a rule of thumb has hitherto been that the thicker the light-storing layer the greater the remanent luminescence. It is true that both the intensity and duration of remanent luminescence increase in proportion with the thickness of the light-storing layer. However, a too thick layer requires copious use of the expensive light-storing pigment, adding to the cost accordingly. It is thus essential that desired light-storing performance be achieved with as thin a light-storing layer as possible.
Ordinary light-storing inks use a light-storing pigment mainly of coarse particles and contain an average of mere 20% or thereabouts of the pigment (on solids basis), and hence do not possess adequate light-storing properties.
Moreover, the luminous, light-storing pigments, each consisting of a mass of hard and large inorganic particles, provide label surfaces rough enough to mar the appearance. The information written on them with a pencil is difficult to erase. Ballpoint and fountain pens are difficult to use because the surfaces repel ink. Felt-tip pens have short life since their tips are rapidly worn out with abrasion by the coarse pigment particles.
The method of adding a light-storing pigment to the liner sheet base as taught by Patent Application Kokai No. 63-117383 is not practical. Since the light-storing pigment is dispersed throughout the resin that constitutes the base, its concentration is so low that the luminous intensity is limited and the remanent luminescence period that permits visual inspection of magnetic tape conditions is as short as about 30 minutes. Even the remanent luminescence makes it hardly possible for the user to read letters and other indications on the tape cassette housing. Moreover, because the light-storing pigment generally consists of coarse particles, a large addition reduces the lubricity characteristics of the liner sheet. The light-storing capacity cannot be increased, therefore, by an abundant use of the pigment; hence the light-emitting time that allows the inspection of tape conditions is limited to only about half an hour.
A further method proposed by EP0700046A2 consists in printing a light-storing ink layer on an appropriate portion of a tape cassette housing with an ink containing a light-storing pigment and making the printed layer surface writable so that the letters and symbols written on it can be read in the dark too. When the article so coated or printed, for example, a tape cassette housing, is transparent, the light disperses in all directions, and merely faint, if any, luminescence results. The limited light emission attracts but scant attention. A light-storing ink is translucent in itself (as the binder for the ink must be as clear as possible to secure ready exposure to light in order to enhance the light-storing performance). Consequently, a thicker coat of the ink extends the light-emitting time but does not increase the luminous intensity accordingly. When a liner sheet surface is printed with an ink containing a light-storing pigment, an excessively thick coat reduces the liner sheet functions. Thus the thickness must be restricted to 100 .mu.m or less, which does not provide sufficient luminous intensity or duration (at least two hours of light-emitting time being essential) for the user to look for the tape cassette or make out letters or other inscriptions on it in the dark.
It is an object of this invention to provide label sheets which overcome the afore-described drawbacks of the prior art and permit the user to grasp the inscribed information exactly at night or in the dark, the label sheets being available at low cost and with excellent writability.
Another object of the invention is to provide light-storing printed articles having a light-storing layer having a remnant fluorescence for a long period of time which permits the users to read the characters or symbols inscribed thereon in a dark place or at night for a long period of time. Here, the printed articles include articles such as tape cassette, protective case for such cassette, on which a light-storing layer is directly printed, and label sheet having a printed light-storing layer thereon and is adapted to be attached to such articles.
A further object of the present invention is to provide a light-storing printed article, on which inscription is directly possible or on which is formed a writable layer which can be writted with a pencil, fountain pen, ball-point pen, aqueous felt pen.
A further object of the present invention is to provide a stronger luminescence with a longer period of time than the prior art so as to allow the users to find the cassettes in a dark place.